Abstract

We describe our efforts to study and compare the ocean-color data derived from the Japanese Ocean Color and Temperature Scanner (OCTS) and the French Polarization and Directionality of the Earth’s Reflectances (POLDER). OCTS and POLDER were both on board Japan’s Sun-synchronous Advanced Earth Observing Satellite from August 1996 to June 1997, collecting approximately 10 months of global ocean-color data. This operation provided a unique opportunity for the development of methods and strategies for the merging of ocean-color data from multiple ocean-color sensors. We describe our approach to the development of consistent data-processing algorithms for both OCTS and POLDER and the use of a common in situ data set to calibrate vicariously the two sensors. Therefore the OCTS- and POLDER-measured radiances are bridged effectively through common in situ measurements. With this approach to the processing of data from two different sensors, the only differences in the derived products from OCTS and POLDER are the differences that are inherited from the instrument characteristics. Results show that there are no obvious bias differences between the OCTS- and POLDER-derived ocean-color products, whereas the differences due to noise, which stem from variations in sensor characteristics, are difficult to correct at the pixel level. The ocean-color data from OCTS and POLDER therefore can be compared and merged in the sense that there is no significant bias between two.

Figures (10)

Spectral bandpass correction factor r(λ) as a function of the sensor-derived two-band ratio values in the normalized water-leaving radiances between wavelengths 490 and 565 nm for (a) the OCTS bands 412, 443, 490, 520, and 565 nm and (b) the POLDER bands 443, 490, and 565 nm. The curves are the least-squares fit.

OCTS-retrieved normalized water-leaving radiance images at wavelengths 443, 490, and 565 nm compared with those derived from POLDER measurements for ocean water over the Sargasso Sea from Nov. 20, 1996 to May 20, 1997. The color scales for [Lw(λ)]N are indicated at the bottom of Fig.
6.

The OCTS-retrieved normalized water-leaving radiance images at wavelengths 443, 490, and 565 nm compared with those derived from POLDER measurements for ocean water over the Bermuda area from Dec. 12, 1996 to June 10, 1997.

Histogram (%) of the OCTS-retrieved normalized water-leaving radiances at wavelengths 443, 490, and 565 nm compared with those from POLDER measurements as in Fig. 5 for (a)–(g) over the Sargasso Sea from Nov. 20, 1996 to Apr. 14, 1997.

Histogram (%) of the OCTS-retrieved normalized water-leaving radiances at wavelengths 443, 490, and 565 nm compared with those from POLDER measurements as for (a) the Sargasso Sea on May 20, 1997 and for (b)–(f) the Bermuda area from Dec. 12, 1996 to June 10, 1997.

OCTS-retrieved chlorophyll a concentration compared with those derived from POLDER measurements for the Sargasso Sea from Nov. 20, 1996 to April 14, 1997. The color scale is indicated at the bottom of Fig.
10.

OCTS-retrieved chlorophyll-a concentration compared with those derived from POLDER measurements for the Bermuda area from Dec. 12, 1996 to June 10, 1997. Some of the in situ measurements, which were acquired at the location near the center of the images, are also indicated as vertical bars in the histograms over the Bermuda area.